1. Field
This disclosure relates to a method for removing a carbonization catalyst from a graphene sheet and a method for transferring the graphene sheet to a substrate or a device.
2. Description of the Related Art
Graphite may comprise a stacked structure of two-dimensional planar sheets in which carbon atoms are bonded in an extended fused array comprising hexagonal rings. A single sheet of the extended fused array, which comprises six-membered carbon rings, may be referred to as graphene.
A graphene sheet, as defined herein, may comprise one or more sheets of graphene. A graphene sheet may have advantageous properties different from those of other materials. In particular, electrons may move on the graphene sheet as if they have zero mass, thus electrons on the graphene sheet may move at the velocity of light in a vacuum. Electron mobility on a graphene sheet has been observed to be from about 20,000 square centimeters per volt seconds (cm2/Vs) to about 50,000 cm2/Vs. Further, a graphene sheet may exhibit unusual half-integer quantum hall effects for electrons and holes.
Since the electrical properties of a graphene sheet, with a given thickness, may change depending on its crystallographic orientation, the electrical properties of the graphene sheet may be controlled by selecting the crystallographic orientation of the graphene sheet. Thus using a graphene sheet devices can be designed to have different electrical properties. The electrical properties of a graphene sheet may be compared with those of a carbon nanotube (“CNT”), which is known to exhibit metallic or semiconducting properties depending on the chirality and diameter of the CNT. A complicated separation process may be desirable in order to take advantage of such metallic or semiconducting properties of CNTs. A graphene sheet may thus have economic advantages over CNTs because a purification process may be avoided, as with synthesized CNTs, thus graphene sheets may be less expensive than CNTs. Therefore, a graphene sheet may be desirable for use in carbon-based electrical or electronic devices.
A graphene sheet may be prepared by a micromechanical process or by a SiC crystal pyrolysis process.
A micromechanical process may include, for example, attaching a tape onto a surface of a graphite sample and releasing the tape from the surface by peeling to remove from the graphite a graphene sheet adhered to the tape. The tape may be then released from the graphene sheet by, for example, dissolving the tape in a solvent.
The SiC crystal pyrolysis process may include, for example, heating a SiC single crystal to decompose SiC on the surface of the crystal. The Si may be removed after the decomposition, and the remaining carbon (C) may form the graphene sheet.